A process control loop is generally comprised of three elements. The first element is a sensor that determines a condition. One example of a sensor is a temperature sensor. The second element typically performs an action. This element may perform a task to alter a condition and may include, for example an actuator that opens a valve to allow more water into a process, or a motor or pump to move an element through a process. The third element is a process control device, for example, a distributed control system (DCS) or programmable logic controller (PLC) coupled between the sensor and the actuator. The process control device receives data from the sensor, and may receive data from the actuator, and makes a decision that causes the actuator to function. Process control devices typically include a computer, controller or a microprocessor chip that executes for example a PID control loop algorithm that operates to maintain a temperature value at a desired setpoint.
Process control loops are known to operate below their expected efficiency, or even malfunction. This malfunction may be caused by a sensor or actuator. In addition, the process control device may receive correct data, but due to a programming problem, may make an improper decision and cause the actuator to take action when it otherwise should not. The process control loop also may operate at a lower efficiency when not properly tuned.
In many applications, a plurality of process control loops are coupled together. As an example a paper mill may include hundreds, if not thousands, of process control loops that are used in the production of paper. In these larger systems it is important for each process control loop to operate properly and efficiently. A malfunction in one process control loop will likely impact the performance of downstream process control loops. Two or more process control loops also may interact with each other. The maintenance and monitoring of the mill's process control loops becomes more complicated as the number of process control loops increases.